Defects in molded containers such as glass bottles and jars are often related to defects in the associated mold of origin. For this reason, it is desirable in an automated operation having a plurality of molds to possess the ability to identify a specific molded container with its mold of origin. The defective mold may then be shut down for repair while the remaining molds continue operation. Alternatively, containers from the defective mold may be automatically sorted as they proceed down the production line.
Mold identification is generally accomplished by molding a mold-identifying code into each container during the forming process. This code may then be read by a suitable scanner for identifying the container with its mold of origin. A number of optical techniques, which find particular utility in conjunction with glass containers, have been proposed for encoding and later reading of the mold-identifying code. For example, in U.S. Pat. No. 3,745,314, light is transmitted axially through a stationary container while the image of a code molded onto the container bottom is rotated past a reading station positioned beneath the container. Encoding and scanning systems which are generally similar in basic concept are illustrated in U.S. Pat. Nos. 3,963,918 and 3,991,883, and in published UK Application Nos. 2,033,120 and 2,017,892. In general, these techniques rely upon refraction of light passing through the code bumps or "lenses," and thus on the optical transmission characteristics of the container material, embody moving optical elements which do not have desired reliability, and/or require the use of end codes on the container for indicating beginning and end of the code to be read. One embodiment disclosed in U.S. Pat. No. 3,963,918 directs light from a rotating light source onto a code molded into the bottom of a container and reads the container code as a function of light energy reflected from the code bumps.
UK Pat. No. 1,580,735 discloses a method and system for mold identification wherein the mold-identifying code is molded into the heel of the container, i.e. at the junction of the container side wall and bottom, as a series of raised integral dot or bar bumps disposed in parallel rows or tracks perpendicular to the container axis. Light energy is transmitted through the container as the latter is rotated about its axis. A scanner is positioned to receive light energy transmitted through the heel of the rotating container. One of the parallel tracks is treated as a timing track to control reading of code data represented in the other track, and the code is read as a function of the refractive characteristic of the timing and code bumps in the adjacent tracks. Again, start and end codes are employed to indicate beginning and end of a scanning operation.
U.S. Pat. Nos. 4,175,236 and 4,230,266 disclose a mold identification technique wherein the mold-identifying code is molded into the container bottom as concentric rings at preselected spacing. A source of diffused light energy is directed through a gradient filter and a lens onto the bottom of the container, with the gradient filter being such that the intensity of light varies linearly as a function of angle of incidence on the container bottom. A camera, which includes an array of photocells parallel to the filter gradient, is positioned to receive light reflected from the container bottom as the container passes over the scanning system, and the mold-specific code is read as a function of the rate of change of light intensity reflected by the leading and trailing edges of the rings.